【作者】 刘军；

【导师】 杨湘杰； 戴斌煜；

【作者基本信息】 南昌大学 ， 材料工程（专业学位）， 2020， 硕士

【摘要】 块体非晶合金(BMGs)具有很高的断裂强度,但是BMG在承力时,高度的局部剪切行为使BMG在没有明显宏观塑性的情况下会直接断裂。这严重限制了 BMG在工程材料领域的应用,因此提升BMG塑性的研究具有非常高的工程应用价值。随着科学技术的发展,人类对材料在性能上的要求越来越高,在非晶合金领域,对非晶合金在性能上的开发还有很多东西需要深入研究。本文从成形工艺与成分设计两方面系统性地研究了 ZrTiNbCuNiBe系非晶复合材料的塑性提升机理和塑性变化规律,以及研究了两种方法之间的作用和联系。对比了铸态和半固态非晶复合材料的微观组织和力学性能的变化,研究了半固态工艺对材料的塑性提升机理。通过正交实验法找到了最优的半固态处理工艺参数以及材料微观组织和性能的变化规律。通过改变合金体系中的Nb含量,研究Nb含量变化对铸态以及最优半固态处理后的复合材料的微观组织和力学性能影响。同时研究Nb含量的变化对半固态工艺塑性提升效果的影响。主要结果如下:(1)半固态处理工艺不会改变Zr54.0Ti13.2Nb4.8Cu7.8Ni6.2Be14.0合金材料的相结构,但微观组织形貌由树枝晶变为球晶。材料的韧性相体积分数和宏观塑性提升,微观硬度降低。其中体积分数和宏观塑性分别提升84%和152%,晶体相硬度降低56%,非晶基底相硬度降低48%。(2)半固态处理时,晶体相的当量直径与保温时间之间遵循奥斯特瓦尔德熟化规律(本文中k=1.84),与保温温度之间为线性关系(本文中其斜率为0.077)。随着Nb含量增加,四种材料的最佳半固态工艺参数分别是(800℃,100min)、(860℃,10min)、(900℃,10min)、(940℃,10min),其最佳温度参数略高于且越来越接近晶体相的固相线。(3)半固态工艺对材料塑性提升机理:工艺可提升晶体相的体积分数,晶体相吸收的变形能增多。工艺可使树枝晶球化和长大,提高韧性相对剪切带的成核能力。大球晶对剪切带被阻碍和增殖都具有积极作用。工艺可降低材料微观硬度,提高微观组织的韧性。(4)Nb含量增加,ZrTiNbCuNiBe系非晶复合材料的韧性相体积分数增加,本研究中半固态Zr60.0Ti14.7Nb5.3Cu5.6Ni4.4Be10.0合金体积分数最大约为60%。相同的半固态工艺参数下,Nb含量增加,球晶当量直径变大,形状因子降低,宏观塑性应变量提升。本文中材料的塑性应变量最大为最优半固态处理后的Zr60.0Ti14.7Nb5.3Cu5.6Ni4.4Be10.0 合金约为 26.3%。(5)Nb含量增加,材料中两相的微观硬度先降低后升高,硬度值最低的是Zr58.5Ti14.3Nb5.2Cu6.1Ni4.9Be11.0合金,非晶基底硬度值高于晶体相。半固态处理后,两相的微观硬度趋于平稳,晶体相的微观硬度都降低,但在非晶基底相中,Zr54.0Ti13.2Nb4.8Cu7.8Ni6.2Be14.0、Zr56.2Ti13.8Nb5.0Cu6.9Ni5.6Be12.5 硬度值降低,Zr58.5Ti14.3Nb5.2Cu6.1Ni4.9Be11.0、Zr60.0Ti14.7Nb5.3Cu5.6Ni4.4Be10.0硬度值升高。(6)Nb含量增加,半固态工艺对材料塑性的提升效果下降,塑性提升率最低降到67.5%。本文的研究内容为Zr基非晶复合材料在工程应用领域的推进具有积极影响。同时可以用作指导Zr基复合材料半固态工艺改善,成分设计优化等工作。更多还原

【Abstract】 Bulk metallic glasses(BMG)has a high fracture strength,but the high local shear behavior of BMG under load causes BMG to break directly without obvious macroscopic plasticity.This severely limits the application of BMG in the field of engineering materials,so the research to improve the plasticity of BMG has very high engineering application value.With the development of science and technology,humans have increasingly higher requirements on the performance of materials.In the field of amorphous alloys,there are still many things that need to be studied for the development of amorphous alloys.This paper systematically studied the plasticity lifting principle and plasticity change law of a series of ZrTiNbCuNiBe amorphous composites material from the aspects of forming technology and composition design,as well as the role and connection between the two methods.The microstructure and mechanical properties of the amorphous composite materials after as-cast and semi-solid treatment were compared,and the principle of plasticity improvement of the semi-solid process on the materials was studied.Through the orthogonal experiment method,the optimal semi-solid processing parameters were found,and the change law of the microstructure and properties of the material was found.By changing the Nb content in the alloy system,the effect of the Nb content change on the microstructure and mechanical properties of the as-cast and composite materials after optimal semi-solid treatment was studied.At the same time,the influence of the change of Nb content on the plasticity improvement effect of the semi-solid process was studied.The main results are as follows:(1)semi-solid isothermal treatment cannot change the phase structure of the Zr54.0Ti13.2Nb4.8Cu7.8Ni6.2Be14.0 alloy,but can change the morphology of the microstructure from dendritic to spherulite.The volume fraction of the ductile phase and the macroplasticity of the material were increased,while the microhardness of the material was decreased.The volume fraction and macroscopic plasticity increased by 84%and 152%respectively,the hardness of crystal phase decreased by 56%and that of amorphous substrate phase decreased by 48%.(2)During semi-solid treatment,the diameter of the crystal phase and the holding time follow the Ostwald ripening law(k=1.84 in this article),and the linear relationship between the crystal phase diameter and the holding temperature(the slope of this article is 0.077).As the Nb content is increased,the optimal semi-solid process parameters of the four materials are(800℃,100min),(860℃,10min),(900℃,10min),(940℃,10min).The parameters are slightly higher and closer to the solid phase line of the crystal phase.(3)The principle of semi-solid process to improve the plasticity of the material:the process can increase the volume fraction of the crystal phase,and the deformation energy absorbed by the crystal phase increases.The process allows the dendrites to become spherical and grow,and improve the toughness relative to the nucleation ability of the shear band.The large-diameter spherulites have a positive effect on the blocking and propagation of the shear band.The process can reduce the hardness of the microstructure of the material and improve the toughness of the microstructure.(4)As the Nb content is increased,the volume fraction of the toughness phase of the ZrTiNbCuNiBe amorphous composite material is improved.In this study,the maximum volume fraction of the toughness phase is 60%of the semi-solid Zr60.0Ti14.7Nb5.3Cu5.6Ni4.4Be10.0 alloy-Under the same semi-solid process parameters,as the Nb content is increased,the diameter of the spherulites is increased,the shape factor is reduced,and the macroscopic plastic strain of the material is improved.The largest plastic strain is the optimal semi-solid Zr60.0Ti14.7Nb5.3Cu5.6Ni4.4Be10.0 alloy,which is about 26.3%in this paper.(5)As the Nb content increases,the microhardness of the two phases in the material first decreases and then increases.The lowest hardness is the Zr58.5Ti14.3Nb5.2Cu6.1Ni4.9Be11.0 alloy.The hardness of the amorphous substrate is higher than that of the crystalline phase.After semi-solid treatment,the microhardness of the two phases tends to be stable,and the microhardness of the crystalline phase decreases,but in the amorphous substrate phase,the hardness of Zr54.0Ti13.2Nb4.8Cu7.8Ni6.2Be14.0,Zr56.2Ti13.8Nb5.0Cu6.9Ni5.6Be12.5 alloy decreases.The hardness of Zr58.5Ti14.3Nb5.2Cu6.1Ni4.9Be11.0 and Zr60.0Ti14.7Nb5.3Cu5.6Ni4.4Be10.0 alloys increased.(6)As the Nb content is increased,the effect of the semi-solid process on the plasticity improvement of the material is reduced,and the plasticity improvement rate is reduced to a minimum of 67.5%.The research content of this article is that the advancement of Zr-based amorphous composite materials in engineering applications has a positive impact.At the same time,it can be used to guide the semi-solid process improvement of Zr-based composite materials and the optimization of composition design.更多还原